Every year, some of the nation's most productive senior prospects fall by the wayside when it comes to the NFL because of concerns ranging from their overall size to system in which they play.

Mike Lombardi, Andrew Brandt and Wes Bunting of nationalfootballpost.com break down the top seniors at each position that still have the most to prove to NFL scouts.

QUARTERBACK: Chase Daniel, Missouri
Daniel is off to a great start, and on a pace to throw for 4,000 yards and 35 touchdowns. But scouts worry about his size – he's listed at 6 feet – and a lack of arm strength. Daniel has struggled throughout his career against big-time competition and will have quite the learning curve going from Missouri's spread offense into a pro-style passing game. Daniel is accurate, and no one questions his production. But how many starting NFL quarterbacks are 6 feet or shorter and came from a spread offense? That's why scouts are concerned.OTHERS: Hunter Cantwell, Louisville; Graham Harrell, Texas Tech.

RUNNING BACK: Arian Foster, Tennessee
Foster possesses an impressive combination of burst and body control for a back of his dimensions. He is averaging 5.2 yards per carry this season and could possibly break Tennessee's career rushing mark. But for a back of his size, Foster (6-1/215) runs too soft between the tackles and plays like a smaller back. This has caused Tennessee to stray from Foster in short-yardage situations in favor of Montario Hardesty. An off-campus fight in 2006 plus injuries to his ankle and knee have worried scouts, but his dip in production and fumbling problems this season have really put a dent in Foster's draft stock. OTHERS: Ian Johnson, Boise State; Marlon Lucky, Nebraska.

WIDE RECEIVER: Louis Murphy, Florida
When you enter the year ranked atop the Blesto and National Scouting rankings at wide receiver, there always is a lot to prove. Such is the case for Murphy. He has a nice combination of size (6-3) and speed (4.35) and has the ability to get vertical and make plays downfield. But he has yet to put up truly respectable numbers in Florida's spread offense. He is off to a slow start again this season, on a pace for only 560 yards. Murphy needs to become a more polished route-runner and learn to sink his hips and dip in and out of breaks. He is simply just a deep threat at this stage and has yet to show he can be successful running every route on the route tree at an NFL-caliber level. OTHERS: Aaron Kelly, Clemson; Brian Robiskie, Ohio State.

TIGHT END: Darius Hill, Ball State
After a sensational junior campaign that included 65 catches and 926 yards receiving, Hill was on the fast track to becoming one of the top senior tight ends in the 2008 draft. But after a pedestrian 4.9 clocking in the 40 at his junior pro day, scouts went back scratching their heads and re-evaluating his tape. With wide receiver Donte Love's career over, Hill has received the brunt of the attention from defenses and is seeing a decline in catches. Hill is a long, angular athlete who lacks power and will never be able to block like a traditional tight end. But his lack of fight and power in jump-ball situations is even more troubling. Hill needs to become more aggressive in all phases of the game and prove to scouts he can do more than just line up in the slot. OTHERS: Travis Beckum, Wisconsin; Anthony Hill, N.C. State.

OFFENSIVE TACKLE: Phil Loadholt, Oklahoma
Loadholt is a massive physical specimen (6-8/338) and possesses long arms and powerful hands. A real mauler in the run game, he can drive defensive ends right out of the picture. And when he locks on in pass protection, the battle is over. But Loadholt lacks flexibility and is too much of a waist-bender. He lacks the foot quickness to reach the corner and struggles re-directing back inside. He is able to get by in college with his length and power, but his lack of athleticism will show up at the next level. Loadholt needs to improve his technique and learn to play with better bend to be successful at the next level. He is best-suited to play the right side in a power-running scheme. OTHERS: Joel Bell, Furman; Andrew Gardner, Georgia Tech.

GUARD: Jeremy Perry, Oregon State
One of the most impressive run-blocking guards in the nation in 2006, Perry displayed a blend of natural leverage and leg drive while absolutely dominating Pac-10 defensive lineman. But a broken leg in the opener derailed his 2007 season. This fall, a knee injury has kept him off the field. Perry is a fluid athlete in space who has a compact stance and good lateral mobility. He is a bit short-armed, but uses his strong upper body and punch to keep linemen off him in pass protection. Perry needs to get on the field and prove to scouts he can stay healthy. Considered at one time a top-60 pick, Perry now looks more like a fringe prospect. OTHERS: Cedric Dockery, Texas; Ray Feinga, BYU.

CENTER: Jon Cooper, Oklahoma Not too many centers in the nation can say they have opened holes for three draftable running backs (Adrian Peterson, Allen Patrick and DeMarco Murray) and have three years' starting experience. But that is the case for Cooper, who uses his savvy, toughness and athleticism to consistently get to the second level in the Sooners' run game. But Cooper is undersized (he's listed at 6-3 and 290) and lacks power in his lower half. He struggles holding the point of attack in pass protection and will need to work in tandem against the massive three-technique tackles in the NFL. Cooper will be limited to zone blocking schemes only, which will cause him to last much longer on draft day then his ability would indicate. OTHERS: Cecil Newton, Tennessee State; A.Q. Shipley, Penn State.

DEFENSIVE END: Tyson Jackson, LSU
He's a powerful, well-built lineman with good girth and length in his upper body. After recording 8.5 sacks as a sophomore, the sky was the limit for Jackson in 2007. But an inconsistent junior campaign left many scouts wondering about his true NFL position. Some seem to think he is best-suited to remain as a base end, where he can use his length and power to hold the point of attack against the run and make the occasional play in the backfield. But his lack of burst and speed around the corner will limit him as a pure pass rusher. Some scouts feel he is best-suited to play inside as a three-technique tackle; others feel the five-technique end position is his best shot. Jackson is a 'tweener, there is no doubt about that. He needs to start showing scouts the same kind of power and aggression that once made him look like a possible first-round pick. OTHERS: Pannel Egboh, Stanford; Tim Jamison, Michigan.

DEFENSIVE TACKLE: B.J. Raji, Boston College
Raji entered the 2007 season as one of the nation's top overall tackles and looked to be headed toward a first-round grade. But he had to redshirt for academic reasons and is back this season. He is a pure nose tackle with a strong lower body and excellent burst off the snap for a man his size (6-1/323). He displays excellent power and leverage at the point of attack, and has the girth to eat up blocks on the inside. His lack of arm length is a bit of a concern, but it is his weight that has scouts worried. Raji played most of the 2006 season at 350-plus pounds, a weight that will be unacceptable in the NFL. Raji has the talent to start at the NFL level. The question: How bad does he want it? OTHERS: Terrill Byrd, Cincinnati; Fili Moala, USC.

LINEBACKER: Jasper Brinkley, South Carolina
He's a physically imposing middle linebacker with excellent overall girth and power. Brinkley is a smooth athlete who can slip blocks and create big-time collisions inside. He is fluid for a big man (6-2/275) and looks like a defensive end at times when he is asked to rush the passer, showcasing an intriguing pass-rush arsenal and a nose for the quarterback. But Brinkley is coming off a knee injury that ended his 2007 season and scouts wonder if he can regain the burst and speed that once made him one of the most lethal linebackers in the SEC. Brinkley is a bit stiff in coverage and doesn't play as physical against the run game as his size would indicate. He is a gifted pass rusher and has some scouts wondering if he could make the transition to outside linebacker in a 3-4 scheme. OTHERS: Orion Martin, Virginia Tech; Scott McKillop, Pittsburgh.

CORNERBACK: Alphonso Smith, Wake Forest
Smith is the total package from an athletic standpoint. He has good burst out his breaks, a compact backpedal and a smooth transition. He makes it tough to get separation and does a great job at the line of scrimmage playing in trail technique. But at 5-9 and 190 pounds, Smith lacks the physical make-up to hold up on the outside against some of the bigger, more physical receivers in the NFL. Smith lacks power and strength and can be easily boxed out in jump-ball situations. His physical limitations will hinder his ability to play man-to-man on the outside, but scouts love his balance, body control and fluidity. He is a great candidate for zone schemes or, at worst, a nickel corner. OTHERS: Domonique Johnson, Jackson State; Morgan Trent, Michigan

SAFETY: Michael Hamlin, Clemson
Hamlin is a long-limbed athlete with good instincts who is asked to play a variety of roles for Clemson's defense. But he doesn't have a true NFL position. He lacks the burst and range to be a free safety and the girth and power to play in the box. Hamlin is being looked at by scouts as a strong safety at this point and could be asked to add some more weight to his 6-2, 205-pound frame. Either way, Hamlin needs to display better re-direction in coverage and better technique as a tackler to warrant more than a mid-round pick. OTHERS: Anthony Scirrotto, Penn State; C.J. Spillman, Marshall.

Nationalfootballpost.com is a new football insider Web site featuring Andrew Brandt, the vice president of the Green Bay Packers for the past nine years, and Michael Lombardi, who has worked in NFL front offices for 22 years - including nine years with Cleveland and eight with Oakland.